External adjustment device for distraction system

ABSTRACT

An external adjustment device includes at least one permanent magnet configured for rotation about an axis with a first handle extending linearly at a first end of the device and a second handle at a second end of the device, the second handle extending in a direction substantially off axis to the first handle. The external adjustment device further includes a motor mounted inside the first handle and a first button located in the proximity to one of the first handle or the second handle, the first button configured to be operated by the thumb of a hand that grips the one of the find handle or second handle. The first button is configured to actuate the motor causing the at least one permanent magnet to rotate about the axis in a first direction.

RELATED APPLICATIONS

The present application is a continuation of U.S. patent application Ser. No. 16/854,499, filed Apr. 21, 2020, which is a continuation of U.S. patent application Ser. No. 16/046,916 filed Jul. 26, 2018 (now U.S. Pat. No. 10,660,675 issued May 26, 2020), which is a continuation of U.S. patent application Ser. No. 14/995,503 filed Jan. 14, 2016, which is a continuation of U.S. patent application Ser. No. 13/172,598 filed Jun. 29, 2011 (now U.S. Pat. No. 9,248,043 issued Feb. 2, 2016), which claims priority to US Provisional Application No. 61/360,353 filed Jun. 30, 2010.

FIELD OF THE INVENTION

The field of the invention generally relates to medical devices for heating disorders of the skeletal astern.

BACKGROUND

Scoliosis is a general term for the sideways (lateral) curving of the spine, usually in the thoracic or thoracolumbar region. Scoliosis is commonly broken up into different treatment groups, Adolescent Idiopathic Scoliosis, Early Onset Scoliosis and Adult Scoliosis.

Adolescent Idiopathic Scoliosis (AIS) typically affects children between ages 10 and 16, and becomes most severe during growth spurts that occur as the body is developing. One to two percent of children between ages 10 and 16 have some amount of Scoliosis. Of every 1060 children, two to five develop curves that are serious enough to require treatment. The degree of scoliosis is typically described by the Cobb angle, which is determined, usually from x-ray images, by taking the most tilted vertebrae above and below the apex of the curved portion and measuring the angle between intersecting lines drawn perpendicular to the top of the top vertebrae and the bottom of the bottom. The term idiopathic refers to the fact that the exact cause of this curvature is unknown. Some have speculated that scoliosis occurs when, during rapid growth phases, the ligamentum flavum of the spine is too tight and hinders symmetric growth of the spine. For example, as the anterior portion of the spine elongates faster than the posterior portion, the thoracic spine begins to straighten, until it curves laterally, often with an accompanying rotation. In more severe cases, this rotation actually create a noticeable deformity, wherein one shoulder is lower than the other. Currently, many school districts perform external visual assessment of spines, for example in all fifth grade students. For those students in whom an “S” shape or “C” shape is identified instead of an “T” shape, a recommendation is given to have the spine examined by a physician, and commonly followed-up with periodic spinal x-rays.

Typically, patients with a Cobb angle of 20.RTM. or less are not treated, but are continually followed up, often with subsequent x-rays. Patients with a Cobb angle of 40.degree. or greater are usually recommended for fusion surgery. It should be noted that many patients do not receive this spinal assessment, for numerous reasons. Many school districts do not perform this assessment, and many children do not regularly visit a physician, so often, the curve progresses rapidly and severely. There is a large population of grown adults with untreated scoliosis; in extreme cases with a Cobb angle as high as or greater than 90.degree. Many of these adults, though, do not have pain associated with this deformity, and live relatively normal lives, though oftentimes with restricted mobility and motion. In AIS, the ratio of females to males for curves under 10.degree. is about one to one, however, at angles above 30.degree., females outnumber males by as much as eight to one. Fusion surgery can be performed on the AIS patients or on adult scoliosis patients. In a typical posterior fusion surgery, an incision is made down the length of the back and Titanium or stainless steel straightening rods are placed along the curved portion. These rods are typically secured to the vertebral bodies, for example with hooks or bone screws, or more specifically pedicle screws, in a manner that allows the spine to be straightened. Usually, at the section desired for fusion, the intervertebral disks are removed and bone graft material is placed to create the fusion. If this is autologous material, the bone is harvested from a hip via a separate incision.

Alternatively, the fusion surgery may be performed anteriorly. A lateral and anterior incision is made for access. Usually, one of the lungs is deflated in order to allow access to the spine from this anterior approach. In a less-invasive version of the anterior procedure, instead of the single long incision, approximately five incisions, each about three to four cm long are made in several of the intercostal spaces (between the ribs) on side of the patient. In one version of this minimally invasive surgery, tethers and bone screws are placed and are secured to the vertebra on the anterior convex portion of the curve. Currently, clinical trials are being performed which use staples in place of the tether/screw combination. One advantage of this surgery in comparison with the posterior approach is that the scars from the incisions are not as dramatic, though they are still located in a visible area, when a bathing suit, for example, is worn. The staples have had some difficulty in the clinical trials. The staples tend to pull out of the bone when a critical stress level is reached.

In some cases, after surgery, the patient will wear a protective brace for a few months as the fusing process occurs. Once the patient reaches spinal maturity, it is difficult to remove the rods and associated hardware in a subsequent surgery, because the fusion of the vertebra usually incorporates the rods themselves. Standard practice is to leave this implant in for life. With either of these two surgical methods, after fusion, the patient's Spine is how straight, but depending on how many vertebra were fused, there are often limitations in the degree of flexibility, both in bending and twisting. As these fused patients mature, the fused section can impart large stresses on the adjacent non-fused vertebra, and often, other problems including pain can occur in these areas, sometimes necessitating further surgery. This tends to be in the lumbar portion of the spine that is prone to problems in aging patients. Many physicians are now interested in fusionless surgery for scoliosis, which may be able to eliminate some of the drawbacks of fusion.

One group of patients in which the spine is especially dynamic is the subset known as Early Onset Scoliosis (EOS), which typically occurs in children before the age of five, and more often in boys than in girls. This is a more rare condition, occurring in only about one or two out of 10,000 children, but can be severe, sometimes affecting the normal development of organs. Because of the fact that the spines of these children will still grow a large amount after treatment, non-fusion distraction devices known as growing rods and a device known as the VEPTR—Vertical Expandable Prosthetic Titanium Rib (“Titanium Rib”) have been developed. These devices are typically adjusted approximately every six months, to match the child's growth, until the child is at least eight years old, sometimes until they are 15 years old. Each adjustment requires a surgical incision to access the adjustable portion of the device. Because the patients may receive the device at an age as early as six months old, this treatment requires a large number of surgeries. Because of the multiple surgeries, these patients have a rather high preponderance of infection.

Returning to the AIS patients, the treatment methodology for those with a Cobb angle between 20.degree. and 40.degree. is quite controversial. Many physicians prescribe a brace (for example, the Boston Brace), that the patient must wear on their body and under their clothes 18 to 23 hours a day until they become skeletally mature, for example to age 16. Because these patients are all passing through their socially demanding adolescent years, it is quite a serious prospect to be forced with the choice of either wearing a somewhat bulky brace that covers most of the upper body, having fusion surgery that may leave large scars and also limit motion, or doing nothing and running the risk of becoming disfigured and possibly disabled. It is commonly known that many patients have at times hidden their braces, for example, in a bush outside of school, in order to escape any related embarrassment. The patient compliance with brace wearing has been so problematic that there have been special braces constructed which sense the body of the patient, and keep track of the amount of time per day that the brace is worn. Patients have even been known to place objects into unworn braces of this type in order to fool the sensor. Coupled with the inconsistent patient compliance with brace usage, is a feeling by many physicians that braces, even if used properly, are not at all effective at curing scoliosis. These physicians may agree that bracing can possibly slow down or even temporarily stop curve (Cobb angle) progression, but they have noted that as soon as the treatment period ends and the brace is no longer worn, often the scoliosis rapidly progresses, to a Cobb angle even more severe than it was at the beginning of treatment. Some say the reason for the supposed ineffectiveness of the brace is that it works only on a portion of the torso, and not on the entire spine. Currently a prospective, randomized 500 patient clinical trial known as BrAIST (Bracing in Adolescent Idiopathic Scoliosis Trial) is enrolling patients, 50% of whom will be treated with the brace and 50% of who will simply be watched. The Cobb angle data will be measured continually up until skeletal maturity, or until a Cobb angle of 50.degree. is reached, at which time the patient will likely undergo surgery. Many physicians feel that the BrAIST trial will show that braces am completely ineffective. If this is the case, the quandary about what to do with AIS patients who have a Cobb angle of between 20.degree. and 40.degree. will only become more pronounced. It should be noted that the “20.degree. to 40.degree.” patient population is as much as ten times larger than the “40.degree. and greater” patient population.

Distraction osteogenesis, also known as distraction callotasis and osteodistraction has been used successfully to lengthen long bones of the body. Typically, the bone, if not already fractured, is purposely fractured by means of a corticotomy, and the two segments of bone are gradually distracted apart, which allows new bone to form in the gap. If the distraction rate is too high, there is a risk of nonunion, if the rate is too low, there is a risk that the two segments will completely fuse to each other before the distinction period is complete. When the desired length of the bone is achieved using this process, the hone is allowed to consolidate. Distraction osteogenesis applications are mainly focused on the growth of the femur or tibia, but may also include the humerus, the jaw bone (micrognathia), or other bones. The reasons for lengthening or growing bones are multifold, the applications including, but not limited to: post osteosarcoma bone cancer, cosmetic lengthening (both legs—femur and/or tibia) in short stature or dwarfism/achondroplasia; lengthening of one limb to match the other (congenital, post-trauma, post-skeletal disorder, prosthetic knee joint), nonunions.

Distraction osteogenesis using external fixators has been done for many years, but the external fixator can be unwieldy for the patient. It can also be painful, and the patient is subject to the risk of pin track infection, joint stiffness, loss of appetite, depression, cartilage damage and other side effects. Having the external fixator in place also delays the beginning of rehabilitation.

In response to the shortcomings of external fixator distraction, intramedullary distraction nails have been surgically implanted which are contained entirely within the bone. Some are automatically lengthened via repeated rotation of the patient's limb. This can sometimes be painful to the patient, and can often proceed in an uncontrolled fashion. This therefore makes it difficult to follow the strict daily or weekly lengthening regime that avoids nonunion (if too fast) or early consolidation (if too slow). Lower limb distraction rates are on the order of one mm per day. Other intramedullary nails have been developed which have an implanted motor and are remotely controlled by an antenna. These devices are therefore designed to be lengthened in a controlled manner, but due to their complexity, may not be manufacturable as an affordable product. Others have proposed intramedullary distractors containing and implanted magnet, which allows the distraction to be driven electromagnetically by an external stator. Because of the complexity and size of the external stator, this technology has not been reduced to a simple and cost-effective device that can be taken home, to allow patients to do daily lengthenings.

SUMMARY

In one embodiment, an external adjustment device includes at least one permanent magnet configured for rotation about an axis. The external adjustment device further includes a first handle extending linearly at a first end of the device and a second handle disposed at a second end of the device, the second handle extending in a direction that is angled relative to the first handle. The external adjustment device includes a motor mounted inside the first handle and a first button located in the proximity to one of the first handle or the second handle, the first button configured to be operated by the thumb of a hand that grips the one of the first handle or second handle. The first button is configured to actuate the motor causing the at least one permanent magnet to rotate about the axis in a first direction.

In another embodiment, an external adjustment device includes at least one permanent magnet configured for rotation about an axis and a motor configured for rotating the at least one permanent magnet about the axis. The external adjustment device includes a first handle extending linearly at a first end of the device and a second handle disposed at a second end of the device, the second handle extending in a direction that is substantially off axis with respect to the first handle, wherein one of the first and second handle comprises a looped shape. A first drive button is located in the proximity to one of the first handle or the second handle, the first drive button configured to be operated by the thumb of a hand that grips the one of the first handle or second handle. The first drive button is configured to actuate the motor causing the at least one permanent magnet to rotate about the axis in a first direction.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an external adjustment device configured to operate a distraction device.

FIG. 2 illustrates a detailed view of the display and control panel of the external adjustment device.

FIG. 3 illustrates the lower or underside surfaces of the external adjustment device.

FIG. 4 illustrates a sectional view of the external adjustment device taken along line 4-4 of FIG. 3 .

FIG. 5 illustrates a sectional view of the external adjustment device taken along line 5-5 of FIG. 3 .

FIG. 6 schematically illustrates the orientation of the magnets of the external adjustment device while driving an implanted magnet of a distraction device.

FIG. 7 illustrates various sensors connected to a printed circuit board of the external adjustment device.

FIG. 8 illustrates a view of the clock positions of Hall effect sensors on the printed circuit board of the external adjustment device.

FIG. 9A illustrates a particular configuration of Hall effect sensors according to one embodiment.

FIG. 9B illustrates output voltage of the Hall effect sensors of the configuration in FIG. 9A.

FIG. 9C illustrates the configuration of FIG. 9A, with the magnets in a nonsynchronous condition.

FIG. 9D illustrates the output voltage of the Hall effect sensors of the configuration in FIG. 9C.

FIG. 10A illustrates a particular configuration of Hall effect sensors according to another embodiment.

FIG. 10B illustrates the output voltage of the Hall effect sensors of the configuration in FIG. 10A.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

FIGS. 1-3 illustrate an external adjustment device 700 that is configured for adjusting a distraction device 1000. The distraction device 1000 may include any number of distraction devices such as those disclosed in U.S. patent application Ser. Nos. 12/121,355, 12/250,442, 12/391,109, 11/172,678 which are incorporated by reference herein. The distraction device 1000 generally includes a rotationally mounted, internal permanent magnet 1010 that rotates in response to the magnetic field applied by the external adjustment device 700. Rotation of the magnet 1010 in one direction effectuates distraction while rotation of the magnet 1010 in the opposing direction effectuates retraction, external adjustment device 700 may be powered by a rechargeable battery or by a power cord 711. The external adjustment device 700 includes a first handle 702 and a second handle 704. The second handle 704 is in a looped shape, and can be used to carry the external adjustment device 700. The second handle 704 can also be used to steady the external adjustment device 700 during use. Generally, the first handle 702 extends linearly from a first end of the external adjustment device 700 while the second handle 704 is located at a second end of the external adjustment device 700 and extends substantially off axis or is angled with respect to the first handle 702. In one embodiment, the second handle 704 may be oriented substantially perpendicular relative to the first handle 702 although other

The first handle 702 contains the motor 705 that drives a first external magnet 706 and a second external magnet 708 as best seen in FIG. 3 , via gearing, belts and the like. On the first handle 702 is an optional orientation image 804 comprising a body outline 806 and an optional orientation arrow 808 that shows the correct direction to place the external adjustment device 700 on the patient's body, so that the distraction device is operated in the correct direction. While holding the first handle 702, the operator presses with his thumb the distraction button 722, which has a distraction symbol 717, and is a first color, for example green. This distracts the distraction device 1000. If the distraction device 1000 is over-distracted and it is desired to retract, or to lessen the distraction of the device 1000, the operator presses with his thumb the retraction button 724 which has a retraction symbol 719.

Distraction turns the magnets 706, 708 one direction and retraction turns the magnets 706, 708 in the opposite direction. Magnets 706, 708 have stripes 809 that can be seen in window 811. This allows easy identification of whether the magnets 706, 708 are stationary or, turning, and in which direction they are turning. This allows quick trouble shooting by the operator of the device. The operator can determine the point on the patient where the magnet of the distraction device 1000 is implanted, and can then put the external adjustment device 700 in correct location with respect to the distraction device 1000, by marking the corresponding portion of the skin of the patient, and then viewing this spot through the alignment window 716 of the external adjustment device 700.

A control panel 812 includes several buttons 814, 816, 818, 820 and a display 715. The buttons 814, 816, 818, 820 are soft keys, and able to be programmed for an array of different functions. In one configuration, the buttons 814, 816, 818, 820 have corresponding legends which appear in the display. To set the length of distraction to be performed on the distraction device 1000, the target distraction length 830 is adjusted using an increase button 814 and a decrease button 816. The legend with a green plus sign graphic 822 corresponds to the increase button 814 and the legend with a red negative sign graphic 824 corresponds to the decrease button 816. It should be understood that mention herein to a specific color used for a particular feature should be viewed as illustrative. Other colors besides those specifically recited herein may be used in connection with the inventive concepts described herein. Each time the increase button 814 is depressed, it causes the target distraction length 830 to increase 0.1 mm. Each time the decrease button 816 is depressed it causes the target distraction length 830 to decrease 0.1 mm. Of course, other decrements besides 0.1 mm could also be used. When the desired target distraction length 830 is displayed, and the external adjustment device 700 is correctly placed on the patient, the operator then holds down the distraction button 722 and the External Distraction Device 700 operates, turning the magnets 706, 708, until the target distraction length 830 is achieved. Following this, the external adjustment device 700 stops. During the distraction process, the actual distraction length 832 is displayed, starting at 0.0 mm and increasing until the target distraction length 830 is achieved. As the actual distraction length 832 increases, a distraction progress graphic 834 is displayed. For example a light colored box 833 that fills with a dark color from the left to the right. In FIG. 2 , the target distraction length 830 is 3.5 mm, and 2.1 mm of distraction has occurred. 60% of the box 833 of the distraction progress graphic 834 is displayed. A reset butted 818 corresponding to a reset graphic 826 can be pressed to reset one or both of the numbers back to zero. An additional button 820 can be assigned for other functions (help, data, etc.). This button can have its own corresponding graphic 828. Alternatively, a touch screen can be used, for example capacitive or resistive touch keys. In this embodiment, the graphics/legends 822, 824, 826, 828 may also be touch keys, replacing or augmenting the buttons 814, 816, 818, 820. In one particular embodiment, touch keys at 822, 824, 826, 828 perform the functions of buttons 814, 816, 818, 820 respectively, and the buttons 814, 816, 818, 820 are eliminated.

The two handles 702, 704 can be held in several ways. For example the first handle 702 can be held with palm facing up while trying to find the location on the patient of the implanted magnet of the distraction device 1000. The fingers are wrapped around the handle 702 and the fingertips or mid-points of the four fingers press up slightly on the handle 702, balancing it somewhat. This allows a very sensitive feel that allows the magnetic field between the magnet in the distraction device 1000 and the magnets 706, 708 of the external adjustment device 700 to be more obvious. During the distraction of the patient, the first handle 702 may be held with the palm facing down, allowing the operator to push the device down firmly onto the patient, to minimize the distance between the magnets 706, 708 of the external adjustment device and the magnet 1010 of the distraction device 1000, thus maximizing the torque coupling. This is especially appropriate if the patient is large or somewhat obese. The second handle 704 may be held with the palm up or the palm down during the magnet sensing operation and the distraction operation, depending on the preference of the operator.

FIG. 3 illustrates the underside or lower surface of the external adjustment device 700. At the bottom of the external adjustment device 700, the contact surface 836 may be made of material of a soft durometer, such as elastomeric material, for example PEBAX® or Polyurethane. This allows for anti-shock to protect the device 700 if it is dropped. Also, if placing the device on patient's bare skin, materials of this nature do not pull heat away from patient as quickly, and so they “don't feel as cold” as hard plastic or metal. The handles 702, 704 may also have similar material covering them, in order to act as non-slip grips.

FIG. 3 also illustrates child friendly graphics 837, including the option of a smiley face. Alternatively this could be an animal face, such as a teddy bear, a horsey or a bunny rabbit. A set of multiple faces can be removable and interchangeable to match the likes of various young patients. In addition, the location of the faces on the underside of the device, allows the operator to show the faces to a younger child, but keep it hidden from an older child, who may not be so amused. Alternatively, sock puppets or decorative covers featuring human, animal or other characters may be produced so that the device may be thinly coveted with them, without affecting the operation of the device, but additionally, the puppets or covers may be given to the young patient after a distraction procedure is performed. It is expected that this can help keep a young child more interested in returning to future procedures.

FIGS. 4 and 5 are sectional views that illustrate the internal components of the external adjustment device 700 taken along various centerlines. FIG. 4 is a sectional view of the external adjustment device 700 taken along the line 4-4 of FIG. 3 . FIG. 5 is a sectional view of the external adjustment device 700 taken along the line 5-5 of FIG. 3 . The external adjustment device 700 comprises a first housing 868, a second housing 838 and a central magnet section 725. First handle 702 and second handle 704 include grip 703 (shown on first handle 702). Grip 703 may be made of an elastomeric material and may have a soft feel when gripped by the hand. The material may also have a tacky feel, in order to aid firm gripping. Power is supplied via power cord 711, which is held to second housing 838 with a strain relief 844. Wires 727 connect various electronic components including motor 840 which rotates magnets 706, 708 via gear box 842, output gear 848, center gear 870 respectively, center gear 870 rotating two magnet gears 852, one on each magnet 706, 708 (one such gear 852 is illustrated in FIG. 5 ). Output gear 848 is attached to motor output via coupling 850, and both motor 840 and output gear 848 are secured to second housing 838 via mount 846. Magnets 706, 708 are held within magnet cups 862. Magnets and gears are attached to bearings 872, 874, 856, 858, which aid in low friction rotation. Motor 840 is controlled by motor printed circuit board (PCB) 854, white the display is controlled by display printed circuit board (PCB) 866 (FIG. 4 ). Display PCB 866 is attached to frame 864.

FIG. 6 illustrates the orientation of poles of the first and second external magnets 706, 708 and the implanted magnet 1010 of the distraction device 1000 during a distraction procedure. For the sake of description, the orientations will be described in relation to the numbers on a clock. First external magnet 706 is turned (by gearing, belts, etc.) synchronously with second external magnet 708 so that north pole 902 of first external magnet 706 is pointing in the twelve o′clock position when the south pole 904 of the second external magnet 708 is pointing in fee twelve o′clock position. At this orientation, therefore, the south pole 906 of the first external magnet 706 is pointing in the six o'clock position while the north pole 908 of the second external magnet 708 is pointing in the six o'clock position. Both first external magnet 706 and second external magnet 708 are turned in a first direction as illustrated by respective arrows 914, 916. The rotating magnetic fields apply a torque on the implanted magnet 1010, causing it to rotate in a second direction as illustrated by arrow 918. Exemplary orientation of the north pole 1012 and south pole 1014 of the implanted magnet 1010 during torque delivery are shown in FIG. 6 . When the first and second external magnets 706, 708 are turned in the opposite direction from that shown, the implanted magnet 1010 will be turned in the opposite direction from that shown. The orientation of the first external magnet 706 and the second external magnet 708 in relation to each other serves to optimize the torque delivery to the implanted magnet 1010. During operation of the external adjustment device 700, it is often difficult to confirm that the two external magnets 706, 708 are being synchronously driven as desired. Turning to FIGS. 7 and 8 , in order to ensure that the external adjustment device 700 is working properly, the motor printed circuit board 854 comprises one or more encoder systems, for example photointerrupters 920, 922 and/or Hall effect sensors 924, 926, 928, 930, 932, 934, 936, 938. Photointerrupters 920, 922 each comprise an emitter and a detector. A radially striped ring 940 may be attached to one or both of the external magnets 706, 708 allowing the photointerrupters to optically encode angular motion. Light 921, 923 is schematically illustrated between the radially striped ring 940 and photointerrupters 920, 922.

Independently, Hall effect sensors 924, 926, 928, 930, 932, 934, 936, 938 may be used as non-optical encoders to track rotation of one or both of the external magnets 706, 708. While eight (8) such Hall effect sensors are illustrated in FIG. 7 it should be understood that fewer or more such sensors may be employed. The Hall effect sensors are connected to the motor printed circuit board 854 at locations that allow the Hall effect sensors to sense the magnetic field changes as the external magnets 706, 708 rotate. Each Hall effect sensor 924, 926, 928, 930, 932, 934, 936, 938 outputs a voltage that corresponds to increases or decreases in the magnetic field. FIG. 9A indicates one basic arrangement of Hall effect sensors relative to sensors 924, 938. A first Hall effect sensor 924 is located at nine o'clock in relation to first external magnet 706. A second Hall effect sensor 938 is located at three o'clock in relation to second external magnet 708. As the magnets 706, 708 rotate correctly in synchronous motion, the first voltage output 940 of first Hall effect sensor 924 and second voltage output 942 of second Hall effect sensor have the same pattern, as seen in FIG. 9B, which graphs voltage for a full rotation cycle of the external magnets 706, 708. The graph indicates a sinusoidal variance of the output voltage, but the clipped peaks are due to saturation of the signal. Even if Hall effect sensors used in the design cause this effect, there is still enough signal to compare the first voltage output 940 and the second voltage output 942 over time. If either of the two Hall effect sensors 924, 938 does not output a sinusoidal signal during the operation or the external adjustment device 700, this demonstrates that the corresponding external magnet has stopped rotating, for example due to adhesive failure, gear disengagement, etc. FIG. 9C illustrates a condition in which both the external magnets 706, 708 are rotating at the same approximate angular speed, but the north poles 902, 908 are not correctly synchronized. Because of this, the first voltage output 940 and second voltage output 942 are now out-of-phase, and exhibit a phase shift (.theta.). These signals are processed by a processor 915 and an error warning is displayed on the display 715 of the external adjustment device 700 so that the device may be resynchronized.

If independent stepper motors are used, the resynchronization process may simply be one of reprogramming, but if the two external magnets 706, 708 are coupled together, by gearing or belt for example, then a mechanical rework may be required. An alternative to the Hall effect sensor configuration of FIG. 9A is illustrated in FIG. 10A. In this embodiment, a third Hall effect sensor 928 is located at twelve o'clock in relation to the first external magnet 706 and a fourth Hall effect sensor 934 is located at twelve o'clock in relation to the second external magnet 708. With this configuration, the north pole 902 of the first external magnet 706 should be pointing towards the third Hall effect sensor 928 when the south pole 904 of the second external magnet 708 is pointing towards the fourth Hall effect sensor 934. With this arrangement, the third Hall effect sensor 928 outputs a third output voltage 944 and the fourth Hall effect sensor 934 outputs a fourth output voltage 946 (FIG. 10B). The third output voltage 944 is by design out of phase with the fourth output voltage 946. An advantage to the Hall effect sensor configuration of FIG. 9A is that the each sensor has a larger distance between it and the opposite magnet, for example first Hall effect sensor 924 in comparison to second eternal magnet 708, so that there is less possibility of interference. An advantage to the Hall effect sensor configuration of FIG. 10A is that it may be possible to make a more compact external adjustment device 700 (less width). The out-of-phase pattern of FIG. 10B can also be analyzed to confirm magnet synchronicity.

Returning to FIGS. 7 and 8 , additional Hall effect sensors 926, 930, 932, 936 are shown. These additional sensors allow additional precision to the rotation angle feedback of the external magnets 706, 708 of the external adjustment device 700. Again, the particular number and orientation of Hall effect sensors may vary. In place of the Hall effect sensors, magnetoresistive encoders may also be used.

In still another embodiment, additional information may be processed by processor 915 and may be displayed on display 715. For example, distractions using the external adjustment device 700 may be performed in a doctor's office by medical personnel, or by patients or members of patient's family in the home. In either case, it may be desirable to store information from each distraction session that can be accessed later. For example, the exact date and time of each distraction, and the amount of distraction attempted and the amount of distraction obtained. This information may be stored in the processor 915 or in one or more memory modules (not shown) associated with the processor 915. In addition, the physician may be able to input distraction length limits, for example the maximum amount that can be distracted at each session, the maximum amount per day, the maximum amount per week, etc. The physician may input these limits by using a secure entry using the keys or buttons of the device, that the patient will not be able to access.

Returning to FIG. 1 , in some patients, it may be desired to place a first end 1018 of the distraction device 1000 proximally in the patient, or towards the head, and second end 1020 of the distraction device 1000 distally, or towards the feet. This orientation of the distraction device 1000 may be termed antegrade. In other patients, it may be desired to orient the distraction device 1000 with the second end 1020 proximally in the patient and the first end 1018 distally. In this case, the orientation of the distraction device 1000 may be termed retrograde. In a distraction device 1000 in which the magnet 1010 rotates in order to turn a screw within a nut, the orientation of the distraction device 1000 being either antegrade or retrograde in patient could mean that the external adjustment device 700 would have to be placed in accordance with the orientation image 804 when the distraction device 1000 is placed antegrade, but placed the opposite of the orientation image 804 when the distraction device 1000 is placed retrograde. Alternatively, software may be programmed so that the processor 915 recognizes whether the distraction device 1000 has been implanted antegrade or retrograde, and then turns the magnets 706, 708 in the appropriate direction when the distraction button 722 is placed.

For example, the motor 705 would be commanded to rotate the magnets 706, 708 in a first direction when distracting an antegrade placed distraction device 1000, and in a second, opposite direction when distracting a retrograde placed distraction device 1000. The physician may, for example, be prompted by the display 715 to input using the control panel 812 whether the distraction device 1000 was placed antegrade or retrograde. The patient may then continue to use the same external adjustment device 700 to assure that the motor 705 turns the magnets 706, 708 in the proper directions for both distraction and retraction. Alternatively, the distraction device may incorporate an RFID chip 1022 which can be read and written to by an antenna 1024 on the external adjustment device 700. The position of the distraction device 1000 in the patient (antegrade or retrograde) is written to the RFID chip 1022, and can thus be read by the antenna 1024 of any external adjustment device 700, allowing the patient to get correct distractions or retractions, regardless of which external adjustment device 700 is used.

While embodiments have been shown and described, various modifications may be made without departing from the scope of the inventive concepts disclosed herein. The invention(s), therefore, should not be limited, except to the following claims, and their equivalents. 

What is claimed is:
 1. A method of monitoring rotation of one or more magnets in an external adjustment device, the method comprising: positioning a first sensor at a first position in relation to a first magnet of the external adjustment device; rotating the first magnet of the external adjustment device about an axis thereof; using the first sensor, sensing a change in a first magnetic field as the first magnet rotates; outputting a time-variable voltage from the first sensor to a processor, the time-variable voltage from the first sensor corresponding to an increase or a decrease in the first magnetic field; and using the processor, analyzing the time-variable voltage output from the first sensor, wherein a time-variable strength of the first magnetic field corresponds to rotation of the first magnet.
 2. The method of claim 1, further comprising: positioning a second sensor at a second position in relation to a second magnet of the external adjustment device; rotating the second magnet of the external adjustment device about an axis thereof; using the second sensor, sensing a change in a second magnetic field as the second magnet rotates; outputting a time-variable voltage from the second sensor to the processor, the time-variable voltage from the second sensor corresponding to an increase or a decrease in the second magnetic field; and using the processor, analyzing the time-variable voltage output from the second sensor, wherein a time-variable strength of the second magnetic field corresponds to rotation of the second magnet.
 3. The method of claim 2, wherein the first sensor is positioned at nine o'clock relative to the axis of the first magnet, and the second sensor is positioned at three o'clock relative to the axis of the second magnet.
 4. The method of claim 1, wherein the analyzing further comprises graphing the time-variable output from the first sensor, and wherein the output voltage from the first sensor varies sinusoidally over time when the first magnet is rotating, and wherein the output voltage from the first sensor does not vary sinusoidally over time when the first magnet is not rotating.
 5. The method of claim 2, wherein the analyzing further comprises graphing the time-variable output from each of the first and the second sensors, and wherein the output voltage from each of the first and the second sensors varies sinusoidally over time when each of the first and the second magnets are rotating.
 6. The method of claim 5, wherein the output voltage from the first or the second sensor does not vary sinusoidally over time when the corresponding one of the first or second magnet is not rotating.
 7. The method of claim 5, wherein the output voltages from the first and the second sensors are in phase when the first and the second magnets are rotating synchronously.
 8. The method of claim 5, wherein a phase shift between the first sinusoidal output and the second sinusoidal output indicates the first magnet and the second magnet are rotating asynchronously.
 9. The method of claim 8, wherein the phase shift further indicates that the asynchronously rotating first and second magnets are rotating at approximately the same angular speed.
 10. The method of claim 1, further comprising displaying the time-variable voltage output of the first sensor on a display of the external adjustment device.
 11. The method of claim 10, further comprising displaying a notification on the display indicating an operating condition of the external adjustment device.
 12. The method of claim 3, further comprising: positioning a third sensor at a third position in relation to the first magnet of the external adjustment device, and a fourth sensor at a fourth position in relation to the second magnet of the external adjustment device; using the third sensor, sensing the change in the first magnetic field as the first magnet rotates; using the fourth sensor, sensing the change in the second magnetic field as the second magnet rotates; outputting a time-variable voltage from each of the third sensor and the fourth sensor to the processor, the time-variable voltage from the third sensor and the fourth sensor corresponding to the increase or the decrease in the first magnetic field and the second magnetic field, respectively; and using the processor, analyzing the time-variable voltage output from the third sensor and the fourth sensor.
 13. The method of claim 12, wherein the third sensor is positioned at twelve o'clock relative to the axis of the first magnet, and the fourth sensor is positioned at twelve o'clock relative to the axis of the second magnet.
 14. The method of claim 12, wherein the analyzing further comprises graphing the time-variable output from each of the third and the fourth sensors, wherein the output voltage from each of the third and the fourth sensors varies sinusoidally over time when each of the first and the second magnets are rotating, and wherein the output voltage from the third or the fourth sensor does not vary sinusoidally over time when the corresponding one of the first or second magnet is not rotating.
 15. The method of claim 14, wherein a phase shift between the third sinusoidal output and the fourth sinusoidal output indicates the first magnet and the second magnet are rotating synchronously.
 16. The method of claim 12, further comprising: positioning a fifth sensor at a fifth position and a sixth sensor at a sixth position in relation to the first magnet of the external adjustment device; using the fifth and the sixth sensors, sensing the change in the first magnetic field as the first magnet rotates; outputting a time-variable voltage from the fifth and the sixth sensors to the processor; wherein the time-variable voltage outputs from the fifth and the sixth sensors correspond to the increase or the decrease in the first magnetic field; positioning a seventh sensor at a seventh position and an eighth sensor at an eighth position in relation to the second magnet of the external adjustment device; using the seventh and eighth sensors, sensing the change in the second magnetic field as the second magnet rotates; outputting a time-variable voltage from the seventh and the eighth sensors to the processor; wherein the time-variable voltage outputs from the seventh and the eighth sensors correspond to the increase or the decrease in the second magnetic field; and using the processor, analyzing the time-variable voltage outputs from the fifth, the sixth, the seventh, and the eighth sensors.
 17. The method of claim 16, wherein the fifth sensor is positioned at ten o'clock relative to the axis of the first magnet, the sixth sensor is positioned at four o'clock relative to the axis of the first magnet, the seventh sensor is positioned at two o'clock relative to the axis of the second magnet, and the eighth sensor is positioned at eight o'clock relative to the axis of the second magnet.
 18. The method of claim 8, further comprising, upon observing the phase shift, resynchronizing the first and the second magnets such that they rotate synchronously.
 19. The method of claim 1, further comprising: positioning a radially striped ring on the first magnet; positioning an optical sensor in proximity to the radially striped ring and the first magnet; using the optical sensor, sensing a change in angular motion of the radially striped ring as the first magnet rotates about the axis; outputting a time-variable voltage from the optical sensor to the processor, the time-variable voltage from the optical sensor corresponding to the change in angular motion of the radially striped ring; and using the processor, analyzing the time-variable voltage output from the optical sensor, wherein the change in angular motion of the radially striped ring corresponds to rotation of the first magnet.
 20. A method of monitoring rotation of one or more magnets in an external adjustment device, the method comprising: implanting a distraction device within a subject's body, the distraction device having an adjustable portion for adjusting a dimension of the distraction device, the adjustable portion comprising a rotatable magnet configured to actuate the adjusting; positioning the external adjustment device in proximity to the rotatable magnet to cause distraction of the distraction device, wherein the external adjustment device comprises a first sensor at a first position in relation to a first magnet of the external adjustment device; rotating the first magnet of the external adjustment device about an axis thereof; using the first sensor, sensing a change in a first magnetic field as the first magnet rotates; outputting a time-variable voltage from the first sensor to a processor, the time-variable voltage from the first sensor corresponding to an increase or a decrease in the first magnetic field; and using the processor, analyzing the time-variable voltage output from the first sensor, wherein a time-variable strength of the first magnetic field corresponds to rotation of the first magnet. 